Well my logic tells me that Applebloom isn't good at growing, so when she goes grow up and discover who she is, she would get a grown apple tree or something to symbolize that.
However, I have a feeling that due to the episode they performed the talent show in, she'll get something in carpentry, or building/furnishing places.

ontopic: I don't want Applebloom to get her cutiemark, because its sorta part of the show, its like fluttershy talking in a non soft voice/being a bitch or spike growing up, they might do something like it for one episode (the spike one where he grows up, the cutie pox SE2EP1/2)